Compilation: fix writeDepFile with no file system inputs

src/Compilation.zig

@@ -4770,12 +4770,12 @@ fn writeDepFile(
 
     try w.print("{f}:", .{bin_file});
 
-    {
+    if (fsi.len > 0) {
         var it = std.mem.splitScalar(u8, fsi, 0);
         while (it.next()) |input| try w.print(" \\\n {f}{s}", .{ prefixes[input[0] - 1], input[1..] });
     }
 
-    {
+    if (fsi.len > 0) {
         var it = std.mem.splitScalar(u8, fsi, 0);
         while (it.next()) |input| try w.print("\n\n{f}{s}:", .{ prefixes[input[0] - 1], input[1..] });
     }